1. Field of the Invention
This invention generally relates to a pump incorporated in a textile package dyeing machine.
2. Description of the Related Art
Yarn for textile manufacturing purposes is commonly wound on perforated tubular cores to form permeable packages through which dye liquor may be circulated for wet processes such as bleaching or dyeing. Both centrifugal pumps and axial flow pumps have been used for circulating dye liquor through textile material in apparatus for dyeing yarn and other textile products. The characteristics of the two types of pumps are dissimilar.
Yarn packages are supported on perforated tubular or fluted spindles on package carriers which may be submersed in dye liquor for treatment. The dyeing process involves the circulation of dye liquor through the yarn, via these supporting spindles, in a machine having provisions for adding dye liquors and chemicals, and of raising the temperature of the dye liquor while periodically reversing the direction of dye liquor flow.
The most level dyeings are obtained by passing the entire volume of dye liquor through the load at least once while increasing the temperature a fixed increment before repeating the sequence in the opposite direction.
Flow of dye liquor from inside the spindle and out through the yarn package around the spindle tends to open up the package and makes penetration of the dye liquor through the package easier. Flow of dye liquor from outside the package and through the package into the spindle tends to compress the package, increasing resistance to dye liquor flow. Therefore, applying the same pressure in both cases does not produce the same rate of bath turnover.
For applications which offer low resistance to flow, axial flow pumps can deliver higher flowrates than centrifugal pumps. Axial flow pumps have been used instead of centrifugal pumps in package dyeing machines, the flow being reversed by reversing the direction of rotation of the axial flow impeller.
Because the axial flow pump performs best against low resistance, system resistance must be reduced to a minimum, as for example by mounting the axial flow impeller vertically inside the machine, directly underneath the package carrier.
However, as conventional direct drive with the electric motor in line with the pump would greatly increase the height of the machine and put the motor directly under the liquor-containing vessel in a location vulnerable to leaks, the motor can be mounted with its axis vertical with the impeller being driven by belts.
Attempts to incorporate an axial flow pump into an external circulating system introduce system resistance and restrict the designer to the alternatives of using double seals and bearings so as properly to support the impeller, or of having to accept a greater than desirable impeller overhang, as well as a sharp change of direction in system pipework if supported only from one end. This sharp change of direction introduces yet more resistance to which the axial flow pump is not suited.
The softer the package, the greater is the difference in density when flow is changed from inside-out to outside-in, and in some circumstances in machines with axial flow pumps, it has been known for outside-in flowrate to fall to zero, and for reversal of dye liquor flow to be discontinued as it served no purpose.
Similarly, in machines for dyeing softly wound packages in open vessels, in which the temperature is raised as closely as possible to the boiling point of water while the direction of flow is periodically reversed, the characteristics of the centrifugal pump favor the maintenance of outside-in flow at the higher temperatures.
The centrifugal pump has been favored in machines dyeing relatively tight packages, or which have external circulating systems offering resistance to dye liquor flow. The axial flow pump has been favored in systems dyeing soft packages, which offer little resistance to flow, so that it follows that in principle the centrifugal pump is better able to deal with the "outside-in" flow condition, and the axial flow characteristics are more suited to the "inside-out" flow condition.
It would not be practical or economical to equip such a machine with two pumps, two circulating systems, and two motors to exploit their different characteristics for the above purposes.